Heart monitoring apparatus

ABSTRACT

An ambulatory heart monitoring apparatus (1) is provided with a slot (3) for receiving an IC card (2). A user places electrodes (7,8) on his body. Operation of a switch (5) causes the apparatus to record EGG signals from the electrodes (7,8) onto the IC card (2). Operation data, including, for example, battery voltage data, data representing the impedance between the electrodes (7,8) and calibration data, are stored on the IC card (2) in association with the recorded ECG signal. The operation data is useful for managing remote subjects. Also the calibration data can be used to normalize the recorded ECG data when it is processed at a remote processing station.

FIELD OF THE INVENTION

The present invention relates to an ambulatory heart monitoringapparatus and a method of heart monitoring.

BACKGROUND TO THE INVENTION

During the testing of some new drugs, it is necessary to monitor theheart of a patient being treated with the new drug. It is inconvenientfor an active patient to be kept in a controlled environment, such as ahospital, during the monitoring. Consequently, patients have beenprovided with heart monitoring equipment which they may take home withthem. Such equipment comprises means for detecting anelectrocardiographic (ECG) signal and a device for transmitting thedetected signals through the public telephone network. If a patientbegins to feel unwell or detects an abnormality in his heartbeat, hemust dial a central station and instruct an operator, at the centralstation, to prepare to record a transmitted ECG signal. This systemsuffers from a number of disadvantages including the problem oflanguage, since drug trials often take place across national boundaries,the non-availability of telephones and poor quality telephone lines.Also, drug companies are wary of becoming directly involved in patientcare which is properly the domain of the patient's physician.

The aforementioned disadvantages may be overcome by replacing thetelephone link by data storage media which may be posted to the centralstation. One known device is the CardioRam produced by ElmedElektromedizinische Gerate. However, this device records ECG signals fora 24 hour period which makes it unsuitable for drug testingmethodologies where intermittent recording is employed over extendedperiods, e.g. a month.

Another device is known from European Patent Application No. 346685which is capable of intermittent recording of ECG signals.

None of the prior art IC card ambulatory heart monitoring apparatusesare entirely suitable for the purpose of apparatus embodying the presentinvention. It is intended that patients will use such apparatusunsupervised. This leads to the problem of ensuring that the patientsuse the apparatus properly and that the apparatus itself is functioningcorrectly.

It is an aim of the present invention to provide an ambulatory heartmonitoring apparatus which is simple enough to meet the market demand ata reasonable cost, whilst providing high quality information on heartfunction.

SUMMARY OF INVENTION

According to a first aspect of the present invention, there is providedan ambulatory heart monitoring apparatus comprising: sensor means fordetecting an electrocardiographic signal; interface means for receivingan IC card and for transferring data thereto; and control meansresponsive to operation of the user input means to cause a block of ECGdata, derived from signals detected by the sensor means during apredetermined period, to be sent to the interface means for storage inan IC card, characterised by means for producing operation data as afunction of an operational parameter of the apparatus wherein thecontrol means causes the operation data to be sent to the interfacemeans for storage in the IC card in association with the ECG data block.

IC card means a card shaped carrier incorporating at least one memory ICand includes smartcards.

The operation data can be characterised as being about the apparatusrather than about the patient. This is data which is useful to determinewhether the apparatus is being used properly and functioning correctly.

Advantageously, the apparatus includes means for producing calibrationdata representive of the calibration state of the apparatus and theoperation data includes the calibration data. Such data can be used tonormalise ECG data to take account of variations between apparatuses orover time.

Conveniently, the apparatus is powered by a battery and includes batteryvoltage sensing means and the operation data includes data representinga sensed battery voltage. This data can be used to normalise ECG data,if necessary, or to provide an indication to the person analysing thedata that a new battery should be fitted.

Conveniently, the sensor means includes two electrodes for contactingwith the body of a subject and detecting means for detecting whether theelectrodes are correctly contacting the body of a subject, and theoperation data includes data indicative of whether the electrodes havecorrectly contacted the body of the patient during detection of an ECGsignal. The electrodes may be of any convenient type. However, theapparatus may be provided with electrodes mounted directly thereon. Theelectrodes may then be positioned to respond to ECG signals by placingthe body of the apparatus against the chest of a subject. This data canbe used to normalise the ECG data or to indicate that a patient requiresfurther tuition.

The detecting means may comprise an impedance measuring means formeasuring the impedance between the electrodes. Preferably, theapparatus includes means whereby the impedance between the electrodes ismeasured at the start and the end of the predetermined period.

Preferably, the IC card is pre-programmed with data comprising a cardID, the card capacity and an IC card battery fitting date.

Data indicating the amount of storage space remaining on the card may becalculated by the apparatus and stored on the card when each newrecording is made.

Preferably, control data is stored on the IC card for controlling theoperation of the apparatus. Such data may comprise a recording durationand an ECG signal sampling rate.

Preferably, an instrument ID code is stored on the IC card, for examplewith each ECG data block.

In an embodiment, the control means is responsive to regime data fromthe interface means to cause a further block of ECG data to be sent tothe interface means, the further block of ECG data being derived from anelectrocardiographic signal detected by the sensor means at a time,defined by said regime data after a preceding detection of anelectrocardiographic signal. The regime data may also include datadefining the number of ECG data blocks to be recorded.

This embodiment enables a plurality of ECG monitoring operations to beperformed at predetermined regular or irregular intervals without theneed for the patient to constantly monitor the time. Thus, ECGrecordings may be made at, for instance, hourly intervals during acritical period automatically once the patient has started the operationof the apparatus.

According to a second aspect of the present invention, there is provideda method of monitoring electrocardiographic signals, comprising thesteps of:

(a) detecting operation of a user input means;

(b) detecting electrocardiographic signals for a predetermined periodusing means for detecting ECG signals;

(c) storing a block of ECG data representing electrocardiographicsignals detected during the predetermined period in an IC card togetherwith associated operation data representing operational parameters ofthe ECG signal detecting means;

(d) transferring the IC card to the data reading station; and

(e) reading the ECG data and operation data from the card.

Preferably, steps (a) to (c) are repeatedly performed before step (d) isperformed. In this case, the following steps may be advantageouslyperformed;

(f) if the user input means is operated for less than a predeterminedduration, displaying the number of spaces available for ECG data blocksleft on the IC card; and

(g) if the user input means is still being operated at the end of saidpredetermined duration continuing with step (b) until the end of thepredetermined period else aborting step (b) and returning to step (a).

Preferably, the method includes the step of:

(h) applying two electrodes to a subject for carrying out step (b).

Preferably, the method includes the step of:

(i) detecting the impedance between the electrodes.

The impedance detection may take place at the beginning or end of saidpredetermined period. Data representing detected impedances isconveniently stored in the IC card as operation data.

Preferably, the method includes the step of:

(j) generating calibration data representing the calibration state of anECG signal detecting means.

The calibration data is conveniently stored in the IC card as operationdata.

Other operation data may be additionally or alternatively stored on theIC card. Such operation data may include the voltage level of a batterypowering the means for detecting ECG signals or of one powering the ICcard.

In an embodiment, step (a) includes reading regime data from the IC cardand repeating steps (b) and (c) in dependence on said regime data.

According to a third aspect of the present invention, there is providedan ambulatory heart monitoring apparatus comprising: sensor means fordetecting an electrocardiographic signal; interface means for receivingan IC card and for transferring data thereto; and control meansresponsive to operation of the user input means to cause a block of ECGdata, derived from signals detected by the sensor means during apredetermined period to be sent to the interface means for storage on anIC card, characterised in that the control means sends an instrument IDcode to the interface means for storage in the IC card.

According to a fourth aspect of the present invention, there is provideda method of monitoring electrocardiographic signals, comprising thesteps of:

(a) detecting operation of a user input means;

(b) detecting electrocardiographic signals for a predetermined periodusing means for detecting ECG signals;

(c) storing a block of ECG data representing electrocardiographicSignals detected during the predetermined period in an IC card togetherwith an instrument ID code;

(d) transferring the IC card to a data reading station; and

(e) reading the ECG data and intrument ID code from the card.

According to a fifth aspect of the present invention, there is providedan electrode comprising a flexible loop including a conductive portion,wherein the conductive portion forms at least part of a radiallyinwardly directed surface portion of the loop.

Preferably, the loop is formed from a strip of flexible material andfastener means, the fastener means being arranged for holding the stripin a loop.

Preferably, the loop is formed from silicone rubber.

Conveniently, the conductive portion is formed from an elastomer loadedwith an electrically conducting substance. The conductive portion ispreferably formed as a separate component and bonded to the loopmaterial. However, it may be formed integrally with the loop material.

Preferably, the electrically conducting substance is nickel. However,other suitable electrically conducting substances, such as silver orcarbon, may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 shows an apparatus according to the first aspect of the presentinvention;

FIG. 2 is a block diagram of the electronic circuit of the apparatusshown in FIG. 1.

FIG. 3 shows a wriststrap electrode according to the third aspect of thepresent invention in its open condition;

FIG. 4 shows the electrode of FIG. 3 in its closed condition; and

FIG. 5 shows an apparatus according to the first aspect of the presentinvention combined with electrodes according to the second aspect of thepresent invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a heart monitoring apparatus comprises a housing 1which encloses the circuitry of the apparatus (not shown). An IC card 2is received within a slot 3 in one wall of the housing 1. A four digit7-segment liquid crystal display (LCD) 4 is mounted in another wall ofthe housing 1 together with a user input means, in the form of a doublepole press-to-make switch 5, and a LED display 6 comprising a yellow LED6a and a green LED 6b. A first electrode 7 and a second electrode 8 arecoupled to the circuitry within the housing 1 by means of respectiveleads 9, 9a which go to a common plug 10.

Referring to FIG. 2, the first and second electrodes 7, 8 are coupled tothe input of a differential amplifier 11. The output of the differentialamplifier 11 is fed to a filter 12. The filter 12 is a low-pass filterhaving a -3db point at approximately 40 Hz. The output of the filter iscoupled to a first input of a multiplexing and analogue-to-digitalconverter circuit 13. The output of the filter 12 is also amplified byan amplifier 14 before being supplied to a second input of themultiplexer and analogue-to-digital converter circuit 13. The output ofthe multiplexing and analogue-to-digital converter circuit 13 is fed toa microprocessor 15 which controls the operation of the apparatus. Thefirst and second electrodes 7, 8 are also coupled to the terminals of animpedance measuring circuit 16 which is driven by a signal from themicroprocessor 15.

An output of the microprocessor 15 is coupled to a memory interface 17which is arranged to receive an IC card 2. The microprocessor 15 is alsocoupled to the LED display 6, an EPROM 18, a RAM 19 and a real timeclock circuit 20.

The real time clock 20 is powered by its own battery 21 and outputs timesignals to a display interface 22 which drives the display 4. Thedisplay interface 22 is also coupled directly to the microprocessor 15.

Operating power for the apparatus is provided by a battery 23. Power issupplied to the functional blocks of the apparatus, including themicroprocessor 15, from the battery 23 via a power control circuit 24.The power control circuit 24 is a latching circuit which operates tosupply power to the microprocessor 15 on momentary operation of theswitch 5, a first pole of which is connected between the battery 23 anda control input of the power control circuit 24.

A battery voltage sensing circuit 25 is arranged for detecting thevoltage of the battery 23 and for providing a signal indicative of thisvoltage to the microprocessor 15.

The operation of the apparatus will now be described. The IC card 2 isinserted into the slot 3 until it is in operating relation with thememory interface 17. The subject then places the first and secondelectrodes 7, 8 on respective wrists.

Operation of the switch 5 causes the power control circuit 24 to supplypower to the microprocessor 15. The microprocessor 15 then begins toperform a control program stored in the EPROM 18. The program stored inthe EPROM 18 may make use of data in the IC card to control theoperation of the apparatus. For instance, the microprocessor 15 may readsampling rate data from the IC card and use this to set the samplingrate of the analogue-to-digital converter circuit 13.

The device hardware is initialized by the microprocessor 15 which alsolights the yellow LED 6a. There is then a short delay of approximately athird of a second, after which the microprocessor 15 applies a signal tothe impedance measuring circuit 16. The impedance measuring circuit 16injects a small current at 10 Hz through the electrodes 7, 8. The signalthus generated is amplified by the differential amplifier 11, filteredby the filter 12 and fed directly to the multiplexing andanalogue-to-digital converter circuit 13. The microprocessor 15 monitorsthe output from the multiplexing and analogue-to-digital convertercircuit 13 and determines an impedance value which is stored in the RAM19. The impedance measurement is then terminated.

The microprocessor 15, then tests for the presence of an IC card 2 inthe slot 3. If no card is detected, the yellow LED 6a is caused to flashfor a period and the monitoring cycle of the device is terminated. If acard is, however, detected the microprocessor accesses the IC card 2 toread certain items of card specific data and any control data. In theembodiment described the card is pre-programmed with data representing acard ID number, a recording interval, the card size and a check sum.However, other data such as an A-to-D sampling rate may also beincluded. The recording interval sets the duration of an ECG monitoringoperation. If the card has already received a recording it will includedata indicating the number of recordings which have been made.

The microprocessor 15 first checks the check sum to ensure that the dataread from the IC card 2 has not been corrupted and that the IC card 2 isof an appropriate type. From the card size and the number of recordingson the card, the microprocessor 15 calculates the number of recordingspaces remaining on the card. This number is then sent, by themicroprocessor 15, via the display interface 22 to be displayed on thedisplay 4. If the IC card is found to be full, operation of the deviceis terminated and the yellow LED 6a is caused to flash for a period.

The microprocessor 15, then accepts a signal from the battery voltagesensor 25, indicating the initial battery voltage. If this voltage isbelow a predetermined level the microprocessor 15 causes the green LED6b to flash to signal a low battery warning.

The microprocessor 15 then commences ECG signal monitoring.

The ECG signals picked up by the electrodes 7,8 are amplified by thedifferential amplifier 11 filtered by the filter 12 and then amplifiedby the amplifier 14 before being supplied to the multiplexer andanalogue-to-digital circuit converter circuit 13. The microprocessor 15takes the data output from the multiplexer and analogue-to-digitalconverter circuit 13 and stores it in the RAM 19.

The microprocessor 15 monitors the passage of time by monitoring thereal time clock 20 and after a period of approximately three secondsfrom the operation of the switch 5, it checks whether the switch 5 isstill being operated. This is performed by monitoring an input which iscoupled to the battery 23 via a second pole of the switch 5. If theswitch 5 has been released the microprocessor 15 sends a signal to thepower control circuit 24 which causes the power control circuit 24 tointerrupt the supply of power to the microprocessor 15, returning it toits dormant state.

If the switch 5 is indeed still being operated after three seconds, theECG monitoring is continued until the end of the period, defined by therecording interval read from the IC card 2. The microprocessor 15determines when the monitoring period is over with reference to the realtime clock 20. Once the ECG monitoring has been completed the impedancebetween the electrodes 7,8 is again determined and the result stored inthe RAM 19.

A calibration operation is then carried out. The microprocessor 15supplies a signal to the calibrating circuit 26 which supplies a 1millivolt peak-to-peak 2 Hz square wave to the input of the filter 12.The microprocessor 15 then detects the signal output by the multiplexingand analogue-to-digital converter circuit 13 and stores it in the RAM19. This value gives an indication of the calibration state of theapparatus. The final battery voltage is then determined and stored inthe RAM 19.

Finally, the microprocessor 15 transfers the data stored in the RAM 19,together with time and date data from the real time clock 20 and aninstrument ID code from the EEPROM 18 to the memory interface 17 whichoutputs it to the IC card 2. The data output to the IC card 2 comprisesthe ECG signal data, calibration data, the initial impedance value, thefinal impedance value, the instrument ID code, a number representing thefinal battery voltage, a date code and a time code. Other data may beincluded as is deemed desirable. For instance, the state of the IC cardbattery may be monitored and data representing this may be stored on theIC card.

The subject can repeat the monitoring operation as the card capacitypermits.

The subject may then remove the IC card from the housing 1, whereupon,the card can be transferred to a central station, e.g. by post, where itis read by a microcomputer system. The operation data, including thecalibration data can be used as necessary to normalize the ECG data. TheECG data read from the IC card can be processed, stored, displayed orprinted as required using conventional techniques.

The term "microprocessor" includes microcontrollers.

The impedance data and battery voltage data can be used in themanagement of a remote subject. For instance, if the battery voltage islow the subject may be instructed to replace the batteries. Theimpedance data indicates whether a subject is applying the electrodesproperly. Therefore, if the measured impedance is high, it may indicatethat the subject requires further tuition in how to use the apparatus.

In an alternative embodiment, the IC card 2 is preprogrammed with datadefining a monitoring regime. This data may define an interval toseparate periods of ECG monitoring and the number of monitoringoperations to be performed.

This embodiment operates substantially in the same manner as theembodiment described above. However, following recording of a firstblock of ECG data, the microprocessor 15 continues to monitor the realtime clock 20 and when it determines that a period, corresponding to theinterval read from the IC card 2, has passed, starts a further ECGmonitoring cycle. This process is repeated until the number ofrecordings made corresponds to the number read from the IC card 2.

Wriststrap electrodes 27, 28 will now be described in more detail withreference to FIGS. 3, 4 and 5.

Each electrode 27, 28 comprises a silicone rubber strip 30. The strip 30is approximately 240 mm long. A first portion 30a of the strip 30 isapproximately 25 mm wide and extends along approximately a third of thelength of the strip from one end thereof. A second portion 30b,comprising the remainder of the strip, is approximately 16 mm wide. Abuckle 31 is secured at the free end of the first portion 30a by meansof a small tab 30c, extending therefrom.

A conductive portion 31, of substantially the same dimensions as thefirst portion 30a of the strip 30, is bonded to the first portion 30a ofthe strip 30. The conductive portion is formed from nickel loadedrubber.

A stud fastener 32 is located towards the free end of the first portion30a of the strip 30 and holds the tab 30c in a loop so as to secure abuckle 34 to the strip 30. A rivet 33 is located towards the other endof the first portion 30a.

The electrode is formed into a loop by passing the free end of thesecond portion 30b of the strip 30 through the buckle. In use, a subjectplaces the strip 30 about a wrist and tightens it by drawing the secondportion 30b of the strip 30 through the buckle 34 so that the conductingportion 31 is in contact with his skin.

We claim:
 1. An ambulatory heart monitoring apparatus comprising:sensormeans for detecting an electrocardiographic signal; interface means forreceiving an IC card and for transferring data thereto; user input meansfor inputting user commands; determining means for detecting operationalparameters of the apparatus and producing operation data in dependencethereon; and control means responsive to operation of said user inputmeans to cause a block of ECG data, derived from signals detected bysaid sensor means during a predetermined period, and said operation datato be sent to the interface means for storage in an IC card.
 2. Anapparatus according to claim 1, including means for producingcalibration data representative of the calibration state of theapparatus, wherein said operation data includes said calibration data.3. An apparatus according to claim 1, wherein the apparatus is poweredby a battery and includes battery voltage sensing means, wherein saidoperation data includes data representing sensed battery voltage.
 4. Anapparatus according to claim 1, wherein the sensor means includes twoelectrodes for contacting the body of a patient and detecting means fordetecting whether said electrodes are correctly contacting the body of apatient, and said operation data includes data indicative of whethersaid electrodes have correctly contacted the body of a patient duringdetection of an ECG signal.
 5. An apparatus according to claim 4,wherein said detecting means comprises an impedance measuring means formeasuring the impedance between said electrodes.
 6. An apparatusaccording to claim 5, including means whereby the impedance between saidelectrodes is measured at the start and at the end of said predeterminedperiod.
 7. An apparatus according to claim 1, including an IC card,wherein the IC card is preprogrammed with data comprising a card ID, arecording period duration and the card capacity.
 8. An apparatusaccording to claim 1, including an analogue-to-digital converter fordigitizing signal output by said sensor means, wherein said controlmeans is responsive to data from said interface means to control thesampling rate of said analogue-to-digital converter.
 9. An apparatusaccording to claim 1, wherein said control means is responsive to regimedata, stored on said IC card and supplied to said control means via saidinterface means to cause a further block of ECG data to be sent to saidinterface means, said further block of ECG data being derived from anelectrocardiographic signal detected by said sensor means at a time,defined by said regime data, after a preceding detection of anelectrocardiographic signal.
 10. An apparatus according to claim 9,wherein the regime data includes data defining a number of ECG datablocks to be recorded.
 11. A method of monitoring electrocardiographicsignals, comprising the steps of:(a) detecting operation of a user inputmeans; (b) detecting electrocardiographic signals for a predeterminedperiod using means for detecting ECG signals; (c) storing a block of ECGdata representing electrocardiographic signals detected during saidpredetermined period in an IC card together with associated operationdata representing at least one operational parameter of the ECG signaldetecting means; (d) transferring said IC card to a data readingstation; and (e) reading said ECG data and said operation data from saidcard.
 12. A method according to claim 11, wherein steps (a) to (c) arerepeatedly performed before step (d) is performed.
 13. A methodaccording to claim 11, including the step of:(h) applying two electrodesto a patient for carrying out step (b).
 14. A method according to claim13, including the step of:(j) generating calibration data representingthe calibration state of said ECG signal detecting means, wherein theoperation data includes said calibration data.
 15. A method according toclaim 13, including the step of:(k) generating voltage datarepresentative of the voltage of a battery powering said means fordetecting ECG signals, wherein the operation data includes said voltagedata.
 16. A method according to claim 13, including the step of:(i)measuring the impedance between the electrodes.
 17. A method accordingto claim 16, wherein impedance measurement takes place at the beginningand at the end of said predetermined period.
 18. A method according toclaim 16, wherein the operation data includes data representing ameasured impedance.
 19. A method according to claim 11, wherein step (a)includes reading regime data from said IC card and steps (b) and (c) arerepeated in accordance with said regime.
 20. A method of monitoringelectrocardiographic signals, comprising the steps of:(a) detectingoperation of a user input means; (b) detecting electrocardiographicsignals for a predetermined period using means for detecting ECGsignals; (c) storing a block of ECG data representingelectrocardiographic signals detected during said predetermined periodin an IC card together with associated operation data representing atleast one operational parameter of the ECG signal detecting means; (d)transferring said IC card to a data reading station; (e) reading saidECG data and said operation data from said card, wherein steps (a) to(c) are repeatedly performed before step (d) is performed; (f) if saiduser input means is operated for less than a predetermined duration,displaying the number of spaces available for ECG data blocks left onsaid IC card; and (g) if said user input means is still being operatedat the end of said predetermined duration continuing with step (b) untilthe end of the predetermined period else aborting step (b) and returningto step (a).
 21. An ambulatory heart monitoring apparatuscomprising:sensor means for detecting an electrocardiographic signal;interface means for receiving an IC card and for transferring datathereto; user input means for inputting user commands; and control meansresponsive to operation of said user input means to cause a block of ECGdata, derived from signals detected by said sensor means during apredetermined period, and an instrument ID code to be sent to theinterface means for storage in an IC card.
 22. A method of monitoringelectrocardiographic signals, comprising the steps of:(a) detectingoperation of a user input means; (b) detecting electrocardiographicsignals for a predetermined period using means for detecting ECGsignals; (c) storing a block of ECG data representingelectrocardiographic signals detected during said predetermined periodin an IC card together with an instrument ID code; (d) transferring theIC card to a data reading station; and (e) reading the ECG data andinstrument ID code from the card.